In zone climate control systems for residential forced air HVAC systems, airflow control valves are installed in air ducts. The airflow control valves can be pneumatically operated through small air tubes or powered and controlled by electrical signals through wires in a cable. When zone systems are installed in existing systems, it is often difficult to find a path for the air tubes or cable from an airflow control valve to the central controller because the ducts are behind walls and ceilings or in the attic or crawlspace.
For retrofit installations, the inside of the existing ducts can provide a path for the tube or cable. The tube or cable needs to be pulled from the airflow control valve through the air duct to a central location such as the discharge plenum of the HVAC blower. This is accomplished by connecting a strong installation blower to the duct system at the central blower plenum and blocking all airflow paths except one so the only airflow path is through the one unblocked air duct to the installation blower. The blower is connected so that air flows from the air duct toward the blower. A parachute about twice the diameter of the air duct is connected to a strong and flexible string and placed in the airflow. The airflow inflates the parachute and quickly pulls the parachute and string through the duct path to the installation blower. The string is then used to pull the tube or cable from the air vent to the central plenum.
The airflow control valves can be installed at the air vents where the air ducts terminate in a room. FIG. 1 illustrates three typical paths from air vents 102, 103, 104 through air ducts to the blower plenum 100. Air ducts 101 can have a round or rectangular cross section and all cross section dimensions are greater than 3xe2x80x3. Duct paths can be over 100 feet long and have several sharp bends such as 114 and 113 where the ducts transition from horizontal to vertical and/or connect to main trunks.
The tubes or cables 110, 111, 112 are typically no more than xc2xcxe2x80x3 in diameter and sufficiently flexible and strong to be pulled through the duct path using the pull string. However, air ducts are often poorly installed and have sharp edges where ducts make turns and connect to trunks.
FIG. 2A illustrates the problem caused by the sharp edge 204 formed by duct 202 making an off-center connection with trunk 203. The pull string 201 has a small diameter and is very flexible, so when pull string 201 pulls tube or cable 200, the pull string makes tight contact with the edge 204. Referring to FIG. 2B, when tube or cable 200 reaches position 211, the tube or cable is obstructed by the edge. Applying additional tension on the pull string can not generate a force that can lift the tube or cable over the edge. Using a rigid device or flexible material to transition from the pull string to the tube or cable does not prevent obstruction because the obstructing edge is sharp. The edge deforms the pull string as the pull string is pulled over the edge. The obstructing edge catches any discontinuity in diameter or change in flexibility.
Using residential HVAC air duct as conduits for tubes or cables is unusual and there is little prior art to teach solutions to passing an obstructing edge. The electrical and communication industry has the most applicable prior art, but the ducts and conduits are designed for cables to be pulled, so obstructing edges are uncommon. Access ports at bends and corners are often provided to limit the length of the pull. Therefore the prior art for cable pulling does not teach how to pass by an obstructing edge. For example, U.S. Pat. No. 5,654,526 issued Aug. 5, 1997 to Sharp describes connectors for conduit sections that provide access for lubrication to reduce the friction when pulling. Patent U.S. Pat. No. 5,029,817 issued Jul. 9, 1991 to Tamm describes a device that includes a roller for installation at a bend in the conduit so the cable can pass by the corner when pulled, but this does not provide a method to pass an obstruction edge. U.S. Pat. No. 5,310,294 issued May 10, 1994 to Perkins describes a connector for connecting a boring devise to a cable for pulling the cable through the hole made by the boring device, but this connector is not adaptable to connecting a pull string to a cable. U.S. Pat. No. 4,078,767 issued Mar. 14, 1978 issued to Battaglia describes a connector for connecting a multi-wire cable to a pull wire. The connector provides a strong, quick, and non-damaging connection, but does not provide a way of passing by an obstructing edge. U.S. Pat. No. 4,552,338 issued Nov. 12, 1985 to Lindgren describes a devise for pushing or pulling a cable through a conduit comprised of many beads with axial holes and helical springs and a connector that connects sections of beads together. This devise is not adaptable for use in a HVAC air duct and provides no method for passing by an obstruction.
The invention is a connector to connect a pull string to a tube or cable. The connector converts the tension force in the pull string to a rotation force about a pivot point between the connector and an obstructing edge so that increasing the tension on the pull string causes rotation about the pivot point until the pivot point becomes unstable and the connector slips by the obstructing edge so that a tube or cable can be pulled by the obstructing edge.